Plastic packages conventionally enclose integrated circuits (IC) to form packaged integrated circuits. Hereinafter, a packaged integrated circuit may be referred to simply as a “package.” Such a package conventionally includes an integrated circuit die typically attached to a die attach pad, a metal leadframe having leads physically isolated from the die attach pad, bond wires which electrically connect pads on the integrated circuit die to individual leads of the leadframe, and a hard plastic encapsulant material which covers part or all of the package components, forms the exterior of the package, protects the integrated circuit from hostile environments, and leaves at least one surface of each lead exposed, thereby enabling electrical connection between the die and a printed circuit board.
In general, IC packages are either leaded or leadless. A leaded package has metal conductors that extend from the package for attaching to a support, such as a printed circuit board. Inside the package the ends of the leads are wire bonded to the bond pads on the die of the IC. In contrast, a leadless package has exposed metal leads on one surface of the outside of the package. The exposed leads are substantially coplanar with the outside surface of the package and the leads are soldered to a support, such as a printed circuit board. The leadless package has a lower profile than the leaded package and generally consumes less space on the support board. Thus, leadless packages are often used when space is a premium as in small systems such as cellular telephones, personal digital assistants and laptop computers.
A problem with conventional IC packages is that bond wires act like inductors, causing energy dissipation from the bond wires. This dissipation results in VCC droop and degraded thermal resistance of the package. Further, when the packaged IC requires higher bit counts, readily available bond wires have diameters that necessitate the usage of multiple bond wires to each lead (e.g., double or triple bonded leads), resulting in higher packaging costs. Still further, conventional leadframe structure for packages (i.e., having leads physically isolated from the die pad) requires a number of bond wires determined by the total number of leads (e.g., one bond wire for each lead), and necessitates certain locking mechanisms to secure the physically isolated leads in the encapsulant of a package body. Such locking mechanisms include, for example, employing recessed surfaces on side surfaces of the physically isolated leads, such recessed surfaces being underfilled by encapsulant material to lock each lead in place within the package body. As used herein, “underfill” and its variants refer to the filling or covering of a downward facing surface (i.e., underside of a surface) formed by one surface being recessed from another surface. The formation of these recessed surfaces by, for example, an etching process is a factor in total packaging costs. As one example, U.S. Pat. No. 6,630,728 shows and describes a plastic integrated circuit package and leadframe for making the package. The package described therein includes only leads physically isolated from the die pad, and for each of these leads, a locking mechanism and a bond wire connection is included.
In a conventional discrete device environment (e.g., the power device/MOSFET field), instead of having all leads physically isolated from a die attach pad, one or more leads are integrally connected to the die attach pad. Heretofore, this discrete environment lead structure has not been used with logic or linear packaged integrated circuits.
Based on the foregoing, a need still exists for an improved technique to package an integrated circuit by employing an enhanced MLP leadframe.